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From "Alexey Diomin (Jira)" <>
Subject [jira] [Issue Comment Deleted] (HIVE-19261) Avro SerDe's InstanceCache should not be synchronized on retrieve
Date Wed, 09 Oct 2019 15:47:00 GMT


Alexey Diomin updated HIVE-19261:
    Comment: was deleted

(was: Update patch
 # readability and prevent multiple time assignment to instance variable
 # remove comments about computeIfAbsent, we can't use it here, because makeInstance can throw
checked exception)

> Avro SerDe's InstanceCache should not be synchronized on retrieve
> -----------------------------------------------------------------
>                 Key: HIVE-19261
>                 URL:
>             Project: Hive
>          Issue Type: Improvement
>            Reporter: Fangshi Li
>            Assignee: Fangshi Li
>            Priority: Major
>         Attachments: HIVE-19261.1.patch
> In HIVE-16175, upstream made a patch to fix the thread safety issue in AvroSerDe's InstanceCache.
This fix made the retrieve method in InstanceCache synchronized. While it should make InstanceCache
thread-safe, making retrieve synchronized for the cache can be expensive in highly concurrent environment
like Spark, as multiple threads need to be synchronized on entering the entire retrieve method.
> We are proposing another way to fix this thread safety issue by making the underlying
map of InstanceCache as ConcurrentHashMap. Ideally, we can use atomic computeIfAbsent in
the retrieve method to avoid synchronizing the entire method.
> While computeIfAbsent is only available on java 8 and java 7 is still supported in Hive,
> we use a pattern to simulate the behavior of computeIfAbsent. In the future, we should
move to computeIfAbsent when Hive requires java 8.

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